The effects of exercise and hormone replacement therapy (HRT) on bone mineral density (BMD) have been investigated by many researchers in a wide variety of subject populations. However, there are relatively few studies on postmenopausal women involving substantial sample sizes that have examined the BMD response to longer-term exercise therapies (greater than or equal to one year). It has been suggested that any therapy that functions to decrease bone remodeling will initially increase BMD solely as a consequence of the bone-remodeling transient. This transient is simply the completion of remodeling packets (formation and mineralization) that were activated prior to the administration of the treatment. Therefore, the true effectiveness of the therapy should be evaluated alter this transient has passed. This underscores the need for longer-term studies of exercise, HRT, or any therapy thought to prevent bone loss. Additionally, despite the general notion that exercise and/or HRT can prevent bone loss, there remains a large number of postmenopausal women who do not respond to the prescribed treatment. Conversely, some women respond much more than would have been predicted based on our current body of knowledge. The aims of this study are to 1) develop statistical models to predict one year through four year changes in regional and total body BMD from nutritional, hormonal, biochemical, body composition, physical activity, and psycho-social variables in post-menopausal women 2) compare the nutritional, hormonal, biochemical, body composition, physical activity, and psycho-social variables in one year BMD responders to one-year BMD non-responders. To accomplish these aims, data from the "Bone, Estrogen, Strength Training" (BEST) study, a large NIH funded project, will be used. The original aim of the BEST study was to determine the effects of a one year exercise training program and HRT on BMD in postmenopausal women. However, many subjects continued on the exercise program after the 1 year study. Sample sizes for I-, 2-, 3-, and 4-year data are 266, 213, 185, and 171 (projected), respectively. This database presents a unique opportunity to examine long-term BMD changes in a comprehensive database which includes the volume of exercise performed, leisure-time physical activity, nutritional data, body composition, physical fitness, hormonal data, markers of bone formation and resorption, and psycho-social variables such as self-esteem, depression, quality of life, social support, and barriers to exercise. The present study will use the existing BEST data as well as the follow-up data for two, three, and four-year effects. The information gained from these analyses will enable the prediction of BMD changes well alter the effects of the bone remodeling transient. Additionally, we will better understand the pattern of the BMD response over longer periods of time and will be able to identify factors that may relate to the likelihood of responding to a given treatment.